LM3351MMX [NSC]
Switched Capacitor Voltage Converter; 开关电容电压转换器
| 型号： | LM3351MMX |
| 厂家： | 
National Semiconductor |
| 描述： | Switched Capacitor Voltage Converter |
| 文件： | 总8页 (文件大小：269K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
December 1999
LM3351
Switched Capacitor Voltage Converter
n 4.2Ω typical step-up output impedance
n 1.8Ω typical step-down output impedance
n 95% typical power conversion efficiency at 50 mA
n 250 nA typical shutdown current
General Description
The LM3351 is a CMOS charge-pump voltage converter
which efficiently provides a 3.3V to 5V step-up, or 5V to 3.3V
step-down. The LM3351 is pin for pin compatible with the
LM3350 but consumes 66% less quiescent current. The
LM3351 uses four small, low cost capacitors to provide the
voltage conversion. It eliminates the cost, size and radiated
EMI related to inductor based circuits, or the power loss of a
linear regulator. Operating power conversion efficiency
greater than 90% provides ideal performance for battery
powered portable systems.
n Low quiescent current extends battary life
Features
n Conversion of 3.3V to 5V, or 5V to 3.3V
n Small Mini SO-8 package
n No inductor required
The architecture provides a fixed voltage conversion ratio of
3/2 or 2/3. Thus it can be used for other DC-DC conversions
as well.
Applications
n Any mixed 5V and 3.3V system
n Laptop computers and PDAs
n Handheld instrumentation
n PCMCIA cards
Key Specifications
n 200 kHz switch frequency allows use of very small,
inexpensive capacitors.
Ordering Information
NSC Package
Package
Order Number
Package Type
Supplied As
Marking
Drawing
MUA08A
MUA08A
LM3351MMX
LM3351MM
Mini SO-8
Mini SO-8
S05A
S05A
3500 Units on Tape and Reel
1000 Units on Tape and Reel
Basic Operating Circuits
Step-Up Converter
Step-Down Converter
DS100146-1
DS100146-2
Connection Diagram
Mini SO8 Package
DS100146-3
Top View
© 1999 National Semiconductor Corporation
DS100146
www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Storage Temperature
−65˚C to +150˚C
260˚C
Lead Temperature (Soldering, 10
secs)
ESD Susceptibility (Note 3)
Not short circuit protected.
2kV
Maximum Input Voltage, Step-Down
Maximum Input Voltage, Step-Up
5.5V
3.65V
Operating Conditions (Note 1)
Power Dissipation (PD) (TA=25˚C,
(Note 2))
500 mW
Ambient Temperature Range
−40˚C to + 85˚C
θja (Note 2)
250˚C/W
150˚C
Tj Max (Note 2)
Electrical Characteristics
3/2 Step-Up Voltage Converter
Specifications in standard type face are for Tj = 25˚C, and those with boldface type apply over full operating temperature
=
range. Unless otherwise specified, Vin = 3.3V, VEnable = 3.3V, Iload = 50 mA, C1, C2, Cin and Cout 1 µF.
Symbol
Parameter
Conditions
Typ (Note 4)
Limits (Note 5)
Units
Vout
Output Voltage at
No Load
Iload = 0 A
5.0
V
NL
Vout
Output Voltage at
50 mA
Iload = 50 mA
4.7
3.3
V
FL
Vin
Input Supply
Voltage Range
V
V(Min)
V(Max)
µA
2.5
3.65
IQ1
Quiescent Current
Quiescent Current
Shutdown Mode, VEnable = 0V,
Iload=0 A; Current into pin Vlow
0.025
1.1
3
µA(Max)
mA
IQ2
Normal Mode, IIoad = 0A; Current into
pin VIow
1.5
6.25
mA(Max)
Ω
Zout
Output Source
Impedance
Iload = 50 mA
4.2
Ω (Max)
kHz
fSW
Switching
(Note 6)
200
Frequency
125
275
kHz(Min)
kHz(Max)
V
VEnable
Enable Threshold
Voltage
1.7
1.0
2.5
V(Min)
V(Max)
µA
IEnable
Leakage Current
Power Efficiency
Current into ENABLE pin; ENABLE =
5V and all other pins at ground
0.025
95
1
µA(Max)
%
Pη
Electrical Characteristics
2/3 Step-Down Voltage Converter
Specifications in standard type face are for Tj = 25˚C, and those with boldface type apply over full operating temperature
=
range. Unless otherwise specified, Vhigh = 5V, VEnable = 5V, Iload = 50 mA, C1, C2, Cin and Cout 1 µF.
Symbol
Parameter
Conditions
Typ (Note 4)
Limits (Note 5)
Units
Vout
Output Voltage at
No Load
Iload = 0 A
3.3
V
NL
Vout
Output Voltage at
50 mA
Iload =50 mA
3.2
5
V
FL
Vin
Input Supply
V
Voltage Range
2.2
5.5
V(Min)
V(Max)
µA
IQ1
Quiescent Current
Shutdown Mode, VEnable = 0V,
Iload=0 A; Current into pin Vhigh
0.25
3
µA(Max)
www.national.com
2
Electrical Characteristics
2/3 Step-Down Voltage Converter (Continued)
Specifications in standard type face are for Tj = 25˚C, and those with boldface type apply over full operating temperature
=
range. Unless otherwise specified, Vhigh = 5V, VEnable = 5V, Iload = 50 mA, C1, C2, Cin and Cout 1 µF.
Symbol
Parameter
Conditions
Typ (Note 4)
Limits (Note 5)
Units
mA
IQ2
Quiescent Current
Normal Mode, IIoad = 0A; Current into
pin Vhigh
0.8
1.0
3
mA(Max)
Ω
Zout
Output Source
Impedance
Iload = 50 mA
1.8
Ω (Max)
kHz
fSW
Switching
(Note 6)
200
Frequency
125
275
kHz(Min)
kHz(Max)
V
VEnable
Enable Threshold
Voltage
1.7
1.0
2.5
V(Min)
V(Max)
µA
IEnable
Leakage Current
Power Efficiency
Current into ENABLE pin; ENABLE =
5V and all other pins at ground
0.025
95
1
µA(Max)
%
Pη
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device is in-
tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The guar-
anteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: For operation at elevated temperatures, LM3351 must be derated based on package thermal resistance of θ and T max, T = T + θ
ja
P .
D
j
j
A
ja
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kW resistor into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.
Note 5: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National’s Averaging Outgoing Quality Level (AOQL).
=
Note 6: The internal oscillator runs at 1.6 MHz, the output switches operate at one eighth of the oscillator frequency, f
8f
.
SW
OSC
Typical Performance Characteristics
Vout vs Iload (Step-Up)
Pη vs Iload (Step-Up)
Output Source Impedance vs
Temperature (Step-Up)
DS100146-4
DS100146-5
DS100146-6
3
www.national.com
Typical Performance Characteristics (Continued)
Vout vs Iload (Step-Down)
Pη vs Iload (Step-Down)
Output Source Impedance vs
Temperature (Step-Down)
DS100146-7
DS100146-8
DS100146-9
Switching Frequency vs
Temperature
DS100146-10
Pin Description
Detailed Operation
Pin
Name
Function
OPERATING PRINCIPLE
1
Cap1+ Positive terminal for the first charge
pump capacitor.
The LM3351 is a charge-pump voltage converter that pro-
vides a voltage conversion ratio of 3/2 in step-up mode and
a conversion ratio of 2/3 in the step-down mode. Thus it can
be used in the step-down mode to provide a 3.3V output
from a regulated 5V input or in the step-up mode to provide
a 5V output from a regulated 3.3V input. Other values of in-
put voltages can be used as long as they are within the lim-
its.
2
3
4
5
Cap1− Negative terminal for the first charge
pump capacitor.
Cap2+ Positive terminal for the second charge
pump capacitor.
Cap2− Negative terminal for the second charge
pump capacitor.
The LM3351 contains an array of CMOS switches which are
operated in a certain sequence to provide the step-up or
step-down of the input supply. An internal RC oscillator pro-
vides the timing signals.
Vlow
In Step-Up mode, this will be the input
terminal. In Step-Down mode, this will
be the output terminal.
Energy transfer and storage are provided by four inexpen-
sive ceramic capacitors. The selection of these capacitors is
explained in the Capacitor Selection section under Applica-
tion Information.
6
7
Gnd
Ground
Vhigh
In Step-Down mode, this will be the
input terminal. In Step-Up mode, this
will be the output terminal.
8
Enable Active high CMOS logic level Enable
Input. Connect to Voltage Input terminal
to enable the IC. Connect to Ground
(Pin 6) to disable.
www.national.com
4
Detailed Operation (Continued)
STEP-UP APPLICATIONS NEED AN EXTRA DIODE
The LM3351 is biased from pin Vhigh. Thus for step-up appli-
cations, an external Schottky diode (D1) is needed to supply
power to Vhigh during startup (See Figure 1). Note that during
shutdown, this diode will provide a DC path from Vin to Vout
.
The load may therefore continue to draw current from the in-
put voltage source. This Schottky diode is not required for
step-down applications (See Figure 2).
SHUTDOWN MODE
When ENABLE is a logic low (ground), the LM3351 enters a
low power shutdown mode. In this mode, all circuitry is dis-
abled and therefore, all switching action stops. During shut-
down, the current consumption drops to 250 nA (typical).
When ENABLE is a logic high, (i.e. 3.3V for step-up mode
and 5.0V for step-down mode), the LM3351 returns to nor-
mal operation.
Application Information
CAPACITOR SELECTION
The LM3351 requires four capacitors: an input bypass ca-
pacitor (connected between Vin and ground), an output hold
capacitor (connected between Vout and ground), and two
sampling capacitors (C1 and C2 in Figures 1, 2). 1.0 µF
±
(
20%) ceramic chip type capacitors are recommended for
all four capacitors. The usable operating frequency should
be greater than 5 MHz for all capacitors.
The output hold capacitor value determines the output ripple.
Increasing the value of the hold capacitor decreases the
ripple. The value of this capacitor (Cout) can be calculated
(approximately) based on the output ripple (∆Vout) require-
ments from:
where Iload is the load current and fO is the oscillator fre-
quency.
In order to ensure superior performance over the entire oper-
ating temperature range, capacitors made of X7R dielectric
material are suggested. However, capacitors made of other
±
dielectric materials that still meet the 20% specification
over the entire temperature range can also be used.
PRECAUTIONS
The LM3351 is not short circuit protected.
5
www.national.com
Typical Application Circuits
DS100146-12
FIGURE 1. Step-Up Converter
DS100146-13
FIGURE 2. Step-Down Converter
Layout Information
LAYOUT CONSIDERATIONS
The LM3351’s high switching frequency (200 kHz) makes a good layout important. Figure 3 illustrates a typical layout. It is im-
portant to keep the distance short between the four capacitors and the IC. Wide traces and grounding are also recommended.
These steps will minimize trace inductance and high frequency ringing. Of the four capacitors, CIN and COUT have the highest
value of di/dt. It is therefore most important to keep them close to the IC. The ground lead that CIN and COUT share should also
be kept wide and short.
The location of the diode (D1) used in the step-up configuration is not critical. This diode is only used during the initial turn on of
the IC. D1 is not needed in step-down applications.
www.national.com
6
Layout Information (Continued)
DS100146-15
B. Actual Size of the Layout
DS100146-14
A. Copper side (5X)
DS100146-16
C. Copper side with Component Locations (5X)
FIGURE 3. Typical Layout
7
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead Mini SO (MM)
Order Number LM3351MMX or LM3351MM
NS Package Number MUA08A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
National Semiconductor
Europe
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
Email: sea.support@nsc.com
www.national.com
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
相关型号：
©2020 ICPDF网 联系我们和版权申明